Brush lifting relay



Sept.-1, 1942. R. M. HEINTZ BRUSH LIFTING RELAY Filed May 10, 1940INVENTOR,

RALPH M. HE/NTZ.

A TTORNEYS Patented Sept. 1, 1942 BRUSH LIFTING RELAY Ralph M. Heintz,Palo Alto, Calif., assignor, by mesne assignments, to Jack 8: Heintz,Inc., Cleveland, Ohio, a corporation of Ohio Application May 10, 1940,Serial No. 334,386

MW 2 Claims. I (Cl. 172- -239) This invention relates to relays forstarting and operating electric motors, and is particularly adapted foruse in such motors as used in connection with engine starters.

Among the objects of this invention are: To provide a means of liftingthe brushes of an engine starter motor, in order to relieve the frictionthereof andto permit the permanent connection of the motor to thestarter so that the inertia of the motor armature may be utilized inaddition to that of a flywheel for providing starting effort; to providea brush-lifting mechanism which, by decreasing the friction on animpulse starter, will permit the same to be hand cranked without thenecessity for disengaging the motor from the starting mechanism: toprovide a starting relay for a small motor which will handle relativelylarge currents without the necessity for either excessive contact areaor excessive pressure; to provide a brush-lifting mechanism and relaywhich has the requisite compactness and lightness to make its usedesirable in aircraft; and, specifically, to provide a starting relayadaptable for use in connection with the starter shown and described inmy copending application, Serial No. 333,376, flied May 4, 1940, nowPatent No. 2,271,640, patented Feb. 3, 1942, to which reference is madefor the description of parts which are not directly pertinent to thepresent invention, but which are used. in connection therewith and uponwhich the present invention is, in part, predicated.

Other objects of this invention will be apparent or will be specificallypointed out in the description forming a part of this specification, butI do not limit myself to the embodiment of the invention hereindescribed, as various forms may be adopted within the scope of theclaims.

In the drawing:

Fig. 1 is an end view, partly in section, of the commutator end of amotor embody ng. the brushlifting mechanism of this invention.

Fig. 2 is a view partly in section, the section line being indicated bythe line 2-2 of Fig. 1.

The impulse type of starter for an airplane engine is utilized in orderthat a relatively small electrical motor may be employed in order tosupply the extremely large power necessary to turn the engine overthrough one or more cycles of. operation until firing occurs and theengine starts. In order to do this, the motor exerts its starting eflortover a relatively long period in order to bring a flywheel up to a speedso high that the energy stored in the flywheel is suincient to supplythe starting effort required. Since the necessity for light weightthroughout the equipment is paramount, the motor should preferablyoperate at as high a speed as possible, and since it is also desirablethat it develop as much power as is possible at these high speeds,

relatively large current must be supplied to it, and this involves largecommutator areas and adequate brush pressure, so that a relatively largepart of the motor power is absorbed in brush friction. When the flywheelhas been brought up to speed the additional torque which would besupplied by the motor upon engaging the starter with the engine isimmaterial, whereas the friction load remains important. Furthermore, inthe event of the failure of starting power, it may be necessary to handcrank the starter. In order to do so, an extremely high gear ratio mustbe used between the hand crank and the flywheel, and in this event thefriction load of the brushes, if they be in contact with the commutator,is so great as to render this practically impossible.

It has been customary, therefore, to disconnect the motor from thestarter when the starter is to be engaged with the engine, or in thecase of hand cranking. This necessitates the provision of a clutchmechanism between the motor and the flywheel, and also eliminates theeffect of the moment of inertia of the motor armature, which would be adesirable addition to the energy stored for supplying the startingtorque.

As has already been indicated, the power demands for a motor of thistype are relatively high, and since it is necessary, in order to meetinstallation demands, that relay starting be employed, a starting relaymust be provided which will handle adequate current. This ordinarilymeans the provision of contacts of large diameter, operated with heavypressure, in order to prevent over-heating, pitting, and sticking, andthis, in turn, means the use of a relatively large amount of power inthe relay circuit. Thus. in order to handle. the current demands of thepresent installation, with a relay of the ordinary type, a contactpressure of at least thirty pounds is indicated, and it will beappreciated that a relay capable of exerting such pressures wouldrequire an appreciable amount of power, and this on anairplane wherepower is precious.

The conditions on a commutator contact are, however, different. It hasrecently been realized that the conduction under a brush. against acommutator is an electronic phenomenon, rather than a solid conductionone, and that the movement of the commutator beneath the brush besidesoifering cooling of the commutator surface also serves by preventing theformation of continuing and growing arcs to maintain an inherentlyunstable electronic discharge in a stab e condition. It is as a resultof this fact that a commutator-brush combination with a pressure ofapproximately one pound will carry the same current that would require athirty pound pressure between stationary contacts, Furthermore, thebrush contacts are necessary to supply the motor in any event, and ifthe brush contacts be used as the starting relay-the necessary result isobtained without introducing additional contact; and additional voltagedrops across such contacts.

Considered in broad terms, therefore, the present invention comprisesthe combination with a commutator and its brushes, having means forholding the brushes against the commutator when the motor is inoperation of means for normally holding the brushes out of contact withthe commutator and electrical relay means for releasing the brushes tobear against the commutator in order to place the motor in operation.

In the showing of the drawing, the housing I within which the commutatorand brush mechanism are mounted forms a continuation of the motor frameor casing 3, and bears upon its end 5 the bearing 1 upon which the motorshaft 9 is journaled. The armature II and commutator l3 are mounted uponthe shaft in the ordinary manner. The housing I is horseshoe shaped, theopen side being covered by a closure l5, formed integral with a fittingll for receiving the electrical connections to the motor, and carryingthe brush and relay mechanism, which therefore may be removed as a wholeby removing the cover plate 15.

Rising from the face of the closure l5 are two supporting posts is,which carry the two brush mechanisms but are insulated therefrom byinsulating strips .20 and bushings 2|. A conducting strip 23, preferablyof brass, lies against the insulating strip for substantially its wholelength, except where it is bent into an arch 25, to which the brushguide 21 is fixed, as, for example, by silver solder, The brush 29slides within the brush guide, and is normally urged against thecommutator by a spring 3|, mounted on an insulated stud 33. Y

The brush is provided with the usual pigtail 35, riveted to the brushand against a lug 3'! which slides within a suitable slot form d in thebrush guide, and the pigtail terminates, at its other end, in aconnecting lug 39.

An insulated bracket arm 41 carries a stub shaft on which thebrush-retracting lever 43 is journaled, this lever extending up towardthe brush to a suilicient distance so that its end can engage the lugs31.

This structure is repeated on both sides of the commutator, the onlydifference being the disposition of the terminal lugs, one of which, asshown on the left of Fig. 1, connects to the motor winding while thatshown on the right of this figure connects to the external circuit.Between the two brush-retractor levers 43 is positioned the solenoid 45of the starting relay.

The solenoid is symmetrical, and within each end a plunger 41 isslidably mounted. The two plungers are similar, and are urged apart by aspring 49, which has suillcient strength to overcome the resistance ofthe brush springs 3|. The plungers are provided at their ends with aflange 5!, which prevents their inner ends coming in contact, and in theflanged end of each there is pressed a button 53 of insulating materialwhich isolates the plungers from the brushretracting levers and preventsthem from shorting the brush mechanism.

The device is actuated by pressing the starter button 55, which excitesthe winding of the solenoid from a battery or other source 51. The twoplungers 41 are thereupon attracted, compressing the spring 49, andreleasing the pressure exerted thereby upon the brush-retracting leversI, so that the brush springs 33 can urge the brushes into contact withthe commutator, completing the motor-circuit in the usual and obviousmanner. The flanges 5| prevent actual contact between the two plungers,which might cause sticking.

When the starting button 55 is released, the two plungers are urgedapart by the spring 4!, pressing against the brush-retractor levers 43,which in turn engage the lugs I! and open the motor circuit bydisengaging the brushes from the commutator.

For the sake of completeness, the complete circuit of motor and relay isincluded schematically in Fig. l. The relay solenoid 45 is excited bythe same battery as supplies the motor, the circuit being completedthrough the motor frame to ground and'thence back to the battery. Themotor circuit through the armature and thence through the series fieldcoils 59 and commutating pole coils 6| is entirely conventional,

I claim:

1. In combination with a commutator, a combined relay andbrush-liiting'mechanism comprising an opposed pair of brush guides,brushes slidably mounted in said guides, to bear on said commutator,resilient means for urging said brushes against said commutator, a pairof electrically operated brush retractors engageable withinstrumentalities on said brushes to positively and simultaneously forcethe brushes out of contact with said commutator, a solenoid mountedbetween said brush retractors, a pair of magnetic plungers slidablymounted within said solenoid; a spring mounted between said plungers tourge them outward against said brush retractors and of suiiicientstrength to overcome the resistance of said resilient means andpositively and simultaneously lift said brushes out of contact with saidcommutator, and means for exciting said solenoid to compress said springand permit the engagement of said brushes with said commutator, saidbrush retractors being of electrical conducting material, and insulatingbuttons atfixed to the ends of said plungers to prevent electricalcontact between said plungers and said brush retractors.

2. In combination with a commutator, a com bined relay and brush-liftingmechanism comprising an opposed pair of brush guides, brushes slidablymounted in said guides to beer on said commutator, resilient means forurging said brushes against said commutator, a pair of electricallyoperated brush retractors engageable with instrumentalities on saidbrushes to positively and simultaneously force the brushes out ofcontact with said commutator, a solenoid mounted between said brushretractors, a pair of magnetic plungers slidably mounted within saidsolenoid, a spring mounted between said plungers to urge them outwardagainst said brush retractors and of suflicient strength to overcome theresistance of said resilient means and positively and simultaneouslylift said brushes out of contact with said commutator, and means forexciting said solenoid to compress said spring and permit the engagementof said brushes with said commutator, said magnetic plungers beingprovided with limiting means at their outer ends for stopping themovement of the plungers as they are shifted toward each other when thesolenoid is energized to compress the spring coacting with the plungers.

RALPH M. HEHN'IZ.

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